Constant Phase

ABSTRACT

Various embodiments are described that relate to a loop with a constant phase. The loop can function as an antenna and be used in object detection. A current source can be used to power the loop such that the loop produces a magnetic field and electric field. The magnetic field can be powerful enough to detect a dielectric while the electric field is so small that it does not interfere with nearby communication equipment. Thus, detection can occur without disruption of other important devices.

GOVERNMENT INTEREST

The innovation described herein may be manufactured, used, imported,sold, and licensed by or for the Government of the United States ofAmerica without the payment of any royalty thereon or therefore.

BACKGROUND

A powered loop antenna can be used to detect a hidden object. Forexample, a person on vacation can use a powered loop antenna functioningas an anomaly detector in an attempt to locate buried objects at abeach. In addition to using the anomaly detector, the person can employa communication device, such as a two-way radio with a child alsoparticipating in the same activity. Thus, a person may want to use adetector device and a communication device concurrently.

SUMMARY

In one embodiment, a system comprises a set of wire sections and a setof reactive compensation elements. The set of wire sections and the setof reactive compensation elements are configured to form a loop poweredby a current provided by a current source operating at about 1 megahertzor above with a source impedance of about 25 ohms or less. Theindividual reactive compensation elements and the individual wiresections of the set of wire sections alternate with one another. The setof reactive compensation elements function to keep a magnitude and aphase of the current substantially uniform throughout the loop. Theloop, when powered by the current, produces a magnetic field that issubstantially greater than an electric field along a longitudinal axisof loop.

In one embodiment, a singular loop antenna comprises a first wiresection, a second wire section that is distinct from the first wiresection, and a third wire section that is distinct from the first wiresection and distinct from the second wire section, where the first wiresection and the third wire section are not contiguous. The singular loopantenna also comprises a first reactive compensation element thatdivides the first wire section from the second wire section and a secondreactive compensation element that divides the second wire section fromthe third wire section and that is distinct from the first reactivecompensation element. The first wire section, the second wire section,the third wire section, the first reactive compensation element, and thesecond reactive compensation element form at least part of a looppowered by a current of at least two amps supplied from a low impedancecurrent source. The singular loop antenna, when supplied with thecurrent, produces a magnetic field that is substantially greater thanthe electric field along a longitudinal axis of the singular loopantenna. The first reactive compensation element offsets an impedance ofthe first wire section and the second reactive compensation elementoffsets an impedance of the second wire section. A magnitude is keepsubstantially constant throughout the loop such that the magnitudechange is not greater than that which is produced by no more than one ofthe wire sections. A phase is keep substantially constant throughout theloop such that the phase change is not greater than that which isproduced by no more than one of the wire sections.

In one embodiment, a system comprises a current source that functions atunder about one ohm with a frequency between about 1 megahertz and 1gigahertz and a singular small loop antenna that is powered by thecurrent. The singular small loop antenna comprises a set of wiresegments that are individually divided by a set of reactive compensationelements such that two individual reactive compensation elements areseparated by a segment of wire and two individual reactive compensationelements are separated by a reactive compensation element. Also, thesingular small loop antenna produces an electric field and a magneticfield such that the magnetic field, that extends substantially normal toa plane of the singular small loop antenna, is substantially greaterthan the electric field and the electric field is of a level that doesnot substantially interfere with communication equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

Incorporated herein are drawings that constitute a part of thespecification and illustrate embodiments of the detailed description.The detailed description will now be described further with reference tothe accompanying drawings as follows:

FIG. 1 illustrates one embodiment of a system comprising a set of wiresections and a set of capacitors,

FIG. 2 illustrates one embodiment of a system comprising a loop and atransistor switch,

FIG. 3 illustrates one embodiment of a system comprising the loop thatinteracts with a tag and an interpretation component,

FIG. 4 illustrates one embodiment of a system comprising a transmissionloop and a reception loop,

FIG. 5 illustrates one embodiment of a system comprising a loop antennaand a current source,

FIG. 6 illustrates one embodiment of a system comprising the loopantenna, an analysis component and a message component.

FIG. 7 illustrates one embodiment of a loop 700 with an x-axis, a y-axisand a z-axis,

FIG. 8 illustrates one embodiment of a system comprising a processor anda non-transitory computer-readable medium,

FIG. 9 illustrates one embodiment of a method comprising seven actions,and

FIG. 10 illustrates one embodiment of a method comprising six actions.

DETAILED DESCRIPTION

A powered loop antenna (e.g., a singular loop or multiple loops) can beemployed that operates from 1 megahertz to 1 gigahertz. In particular,powered small loop antennas can be employed where the antenna size isless than a ¼ wavelength in size, in which the currents along aconductor of the antenna are mostly in phase. Symmetry of the loopantenna can be such that a propagating electromagnetic (EM) field (e.g.,a transverse EM field) is not produced normal to the loop. Instead, aradiation pattern can peak in directions in the plane of the loop. Sincecancellation may not be complete (e.g., due to the phase differencebetween the arrival of the wave at the near and far sides of the loop) asimilar argument may not apply to signals received in that plane (e.g.,that voltages induced by an impinging radio wave would cancel along theloop). A small (e.g., <¼ λ) magnetic loop antenna can be circular withthe feed point at one end. A variable air capacitor can be inserted atthe top opposite the feed point for matching to 50Ω. An antenna withthis configuration can have a high quality with narrow bandwidths ofonly a few kilohertz. A primary goal of this type of antenna can be toprovide an effective radiator with a good far field pattern.

Aspects disclosed herein can be used to optimize an antenna design toproduce an antenna with very strong magnetic near fields. A small loopantenna can be divided into k sections (with k as an integer) and caninclude a reactive compensation element for controlling generation of alocal magnetic field between sections. The reactive compensation elementcan be coupled to one of the k sections and having a reactance thatsubstantially cancels the series reactance of a section at an operatingfrequency.

A powered loop antenna can be constructed and deployed that combines alow impedance current source (e.g., a source impedance of about 1 ohm)with a low real impedance reactively compensated loop antenna designedto operate at a frequency or set of frequencies between 1 megahertz and1 gigahertz. Operation of a sensor (e.g., powered loop antenna) can bedependent on a magnetic field that is projected and that in turn isdirectly related to the current in the magnetic current loop. In oneexample, a 50 ohm amplifier can benefit from matching resulting in anarrow bandwidth and excessive operational sensitivity. A radiofrequency (RF) current source can provide a bandwidth of greater than10%. This can allow for greater flexibility of mounting configurations.Using a 50 ohm power amplifier with the powered loop antenna can benefitfrom a matching network to transform from 50 ohms to approx. 1±j3 ohms.Thus, a voltage controlled current source can feed to a 50 ohm poweramplifier which is then impedance matched to 1±j3 ohms. This process canprovide for a maximum bandwidth of about 1% and results in relativelypoor efficiency. Use of a RF current source and/or a RF power amplifierthat drives a low impedance magnetic sensor can result in a minimum of a10× increase in bandwidth and approximately a 5-10× reduction in powerwith the sensor operating at approx. 1±j3 ohms. This type of sensor canpenetrate the ground to detect deeply buried threats, such as landmines,etc., while its design reduces unwanted electromagnetic (EM)interference. Applications of such a sensor (e.g., powered loop antenna)can include metal/anomaly sensors, induction charging (e.g., wirelesscharging) systems, communication with active or passive tags, etc.

A large magnetic field can be transmitted while minimizing generation ofa propagating EM wave can be done by use of a current loop in which thecurrent around the loop has a constant magnitude and a constant phase. Aconventional current loop sensor can have the current change phasearound the loop and this phase change generates a propagating EM signal.By keeping both the magnitude and phase constant, little EM signal isprojected, but a strong magnetic signal is produced that extends normalto the plane of the loop creating a large magnetic field in the nearfield. This field can penetrates conducting dielectrics such as groundwhich have little effect on the magnetic field but substantiallyterminate the electric field and thus, a propagating EM wave. In oneembodiment an in-phase current loop is created using multiple smallloops. In one embodiment, an in-phase current loop design can be builtin which reactive compensation is used. Periodic series capacitors canbe placed around the loop to compensate for time-of-flight phase changealong a segment of the loop. Thus a magnetic current loop can be used ina magnetic-current-loop-based communication system. In one embodiment,the loop can be divided into small segments and a reactive compensationelement can be added to the segments. Adding reactive compensation tothe segments of the loop cancels series reactance of the segment of theloop and provides for current magnitude and phase uniformity along theloop at a given instant in time. Therefore, a loop can be created withimpedance at 13.56 megahertz that is around 1±j3 ohms.

Therefore, as with the standard small loop antenna in which the currentis mostly in phase around the loop, a design implementing aspectsdisclosed herein can force the current to be even more in phase. Currentloop antennas can provide for narrowband operation due to the use of theimpedance tuner to transform from the low real impedance of the loop(around a few ohms) to the 50 ohm impedance of an RF generator. Thistransformation process can reduce the bandwidth of a system. A highpower detector can be used to locate objects underground, whether theseobject are metal or of a dielectric material. To achieve this level ofdetection a relatively strong current source can be used, such as asource producing about an amp or greater of current. This strong currentsource can produce a relatively strong magnetic field that can be usedto facilitate the detection. However, this strong current source canalso produce a relatively strong electric field. The relatively largeelectric field can disrupt nearby equipment, such as communicationdevices.

Therefore, it can be desirable in at least some circumstances to have adetector that produces a relatively strong magnetic field with arelatively weak electric field. In other words, it can be desirable toemploy a detector capable of detecting metal and/or a dielectric whilenot substantially impacting a communication device or other nearbydevices. In order to do this, the detector can include a set wiresegments separated by a set of capacitors configured as a loop. Thisconfiguration can enable the phase to be constant throughout the loop.The capacitors can be set at values to reduce and/or minimize theelectric field.

The following includes definitions of selected terms employed herein.The definitions include various examples. The examples are not intendedto be limiting.

“One embodiment”, “an embodiment”, “one example”, “an example”, and soon, indicate that the embodiment(s) or example(s) can include aparticular feature, structure, characteristic, property, or element, butthat not every embodiment or example necessarily includes thatparticular feature, structure, characteristic, property or element.Furthermore, repeated use of the phrase “in one embodiment” may or maynot refer to the same embodiment.

“Computer-readable medium”, as used herein, refers to a medium thatstores signals, instructions and/or data. Examples of acomputer-readable medium include, but are not limited to, non-volatilemedia and volatile media. Non-volatile media may include, for example,optical disks, magnetic disks, and so on. Volatile media may include,for example, semiconductor memories, dynamic memory, and so on. Commonforms of a computer-readable medium may include, but are not limited to,a floppy disk, a flexible disk, a hard disk, a magnetic tape, othermagnetic medium, other optical medium, a Random Access Memory (RAM), aRead-Only Memory (ROM), a memory chip or card, a memory stick, and othermedia from which a computer, a processor or other electronic device canread. In one embodiment, the computer-readable medium is anon-transitory computer-readable medium.

“Component”, as used herein, includes but is not limited to hardware,firmware, software stored on a computer-readable medium or in executionon a machine, and/or combinations of each to perform a function(s) or anaction(s), and/or to cause a function or action from another component,method, and/or system. Component may include a software controlledmicroprocessor, a discrete component, an analog circuit, a digitalcircuit, a programmed logic device, a memory device containinginstructions, and so on. Where multiple components are described, it maybe possible to incorporate the multiple components into one physicalcomponent or conversely, where a single component is described, it maybe possible to distribute that single component between multiplecomponents.

“Software”, as used herein, includes but is not limited to, one or moreexecutable instructions stored on a computer-readable medium that causea computer, processor, or other electronic device to perform functions,actions and/or behave in a desired manner. The instructions may beembodied in various forms including routines, algorithms, modules,methods, threads, and/or programs including separate applications orcode from dynamically linked libraries.

FIG. 1 illustrates one embodiment of a system 100 comprising a set ofwire sections 1-8 and a set of capacitors a-h. The capacitors a-h canfunction as example reactive compensation elements. The set of wiresections 1-8 and the set of capacitors a-h are shown as forming a loop(e.g., a rectangular loop) with the individual capacitors of the set ofcapacitors a-h and the individual wire sections 1-8 alternating with oneanother. The individual capacitors of the set of capacitors a-h can besubstantially evenly distributed (e.g., equidistant) from themselves andbe configured to be in series around the loop. The loop can be supplieda current from a current source. The set of capacitors a-h can functionto keep a magnitude and a phase of the current substantially uniformthroughout the loop. In one embodiment, the current can be at leastabout one amps operating at about 1 megahertz or above with a sourceimpedance of about 25 ohms or less and in turn the loop produces anelectric field that is substantially less than the magnetic field.

The magnetic field can be of a sufficient strength to detect a metaland/or to detect a dielectric. The magnetic field extends about onewavelength from the loop, such as a wavelength is about twenty-twometers (e.g., a wavelength that corresponds to a frequency of about13.56 megahertz (MHz)). In one embodiment, the loop can performtransmission and/or reception functions. The loop can be a small loopantenna.

Aspects disclosed herein can be used to improve and/or optimize antennadesign such that the antenna produces a strongest magnetic near tomid-field as possible for forward detection of metal objects or otherobject. Further, the antenna can be used to transfer power andinformation between microelectronic devices. The H-Field associated withthe antenna can be relatively high and a drop off can be about 1/r²(e.g., r=radius). In one example, the frequency of operation for thesystem 100 can be from about 1 MHz to about 1 Gigahertz (e.g., about13.56 MHz). To keep the size of the system 100 relatively small thesmall loop antenna configuration can be employed.

Currents along a conductor of the system 100 can be mostly in phase.Symmetry of the system 100 can allow for a propagating electromagnetic(EM) field (e.g., a transverse EM field) that is not produced normal tothe loop. Instead, a radiation pattern can peak in directions in theplane of the loop. For signals received in that plane (e.g., voltagesinduced by an impinging radio wave would cancel along the loop) this maynot occur since cancellation may not be complete due to the phasedifference between an arrival of the wave at the near and far sides ofthe loop. A conventional small (<¼ λ) (e.g., λ=wavelength) magnetic loopantenna can be circular with the feed point at one end. This circularantenna can include a variable air capacitor at a top opposite with afeed point for matching to 50Ω. The conventional antenna can have veryhigh Q-factor with narrow bandwidths of only a few kilohertz. Thus, thistype of antenna may be able to provide an effective radiator with a goodfar field pattern but poor near or middle field pattern.

Aspects disclosed herein can be used to optimize antenna design toproduce very strong magnetic near fields. The small loop antenna can bedivided into k sections, where k is an integer, and a reactivecompensation element set (e.g., capacitors a-h) can be employed forcontrolling generation of the local magnetic field between the wiresections 1-8. The reactive compensation element can be coupled to one ofthe k sections and having a reactance that substantially cancels theseries reactance of each section of the wire sections 1-8 at anoperating frequency. Therefore, as with the standard small loop antennain which the current is mostly in phase around the loop, the system 100can force the current to be even more in phase.

The system 100 can have the current with a constant magnitude andconstant phase. This current can cause the system 100 to produce a largemagnetic field while minimizing a generation of a propagating EM wave.Absent the set of capacitors a-h the current changes phase around theloop and this phase change generates a propagating EM signal. By keepingboth the magnitude and phase constant, relatively little EM signal isprojected, but a strong magnetic signal is produced that extends normalto the plane of the loop creating a large magnetic field in the nearfield. This large magnetic field can penetrate conducting dielectricssuch as ground which have little effect on the magnetic field butsubstantially terminate the electric field and thus, a propagating EMwave. Periodic series capacitors placed around the loop compensate forthe time-of-flight phase change along a segment of the loop. As thephase changes while the current passes through an individual wiresection of the system 100 and individual capacitor of the system 100undoes the phase change.

In one embodiment, the system 100 can be used in amagnetic-current-loop-based communication system. The system 100 isdivided into small segments and reactive compensation is added to eachsegment, such as by an individual capacitor. Adding reactivecompensation to segments of the loop cancels the series reactance of thewire section and provides for current magnitude and phase uniformityalong the loop at an instant in time.

The large magnetic field can be transmitted while minimizing thegeneration of the propagating EM by using the loop such that the currentaround the loop has a constant magnitude and a constant phase. Withoutthe set of capacitors a-h current of a capacitor-less loop would changephase around the capacitor-less loop and this phase change wouldgenerate a propagating EM signal that could interfere with communicationequipment. By keeping both the magnitude and phase constant in the loopas the system 100 relatively little EM signal can be projected but astrong magnetic signal can be produced that extends normal to a plane ofthe loop creating a large magnetic field in the near field. This fieldcan penetrate conducting dielectrics such as ground which have littleeffect on the magnetic field but substantially terminate the electricfield and thus a propagating EM wave. An in-phase current loop can becreated using multiple loops or a singular loop.

Aspects disclosed herein can have applicability in various industriesand/or products. In one example, devices that respond to a magnetic wave(e.g., change state, become jammed, etc.) can be triggered by practiceof aspects disclosed herein. In one example, hobbyists can use adetector built in accordance with aspects disclosed herein for artifactcollection. In one example, a detector can be built in accordance withaspects disclosed herein and used in construction to detect objectsunderground before digging.

In one embodiment, unique phase characteristics can appear in theresponse from an interrogated object (e.g., a target) excited with themagnetic during exposure to the magnetic field and/or after magneticfield is removed. Altering a pulse shape can force leading and middlesections of the pulse to induce unique phase information. Thisalteration can be done by the interrogated object either passively,semi-passively, or actively. In one embodiment, the interrogated objectcan be a passive object, (e.g., an asset management tag or landmine)that can have a prescribed response (e.g., landmine detonation)imparting a prescribed phase characteristic in a trailing response. In asemi-passive example the tag (e.g., a tag powered by a battery) canrectify an applied magnetic field pulse and impart digital informationin the falling phase response by, for example, superimposing informationon a trailing edge by opening and closing a loop antenna, or otherantenna. In an active example, the tag can be self-powered and canactively alter its characteristics in the trailing edge of the magneticpulse to impose digital information in the phase response. In oneembodiment, the tag can be powered by a battery.

FIG. 2 illustrates one embodiment of a system 200 comprising a loop 210and a transistor switch 220 (e.g., the transistor switch can be part ofthe tag). In one embodiment, the loop 210 is the system 100 of FIG. 1.The transistor switch 220 can be configured to alter characteristics ofthe loop 210 (e.g., when the loop functions as a small loop antenna) ina binary manner such that direct current is produced to power an activecircuit (e.g., active circuit connected to the tag). In one example, theloop 210 rectifies a current to provide direct current that powers anactive circuit. The tag can alter the antenna characteristics, forexample using the transistor switch 210, to change the characteristicsof a loop antenna. If the antenna characteristics are altered in abinary fashion then binary information can be returned to a reader in atrailing phase characteristic.

FIG. 3 illustrates one embodiment of a system 300 comprising the loop210 interacting with a tag 310 (e.g., the tag 310 can retain thetransistor switch 220 of FIG. 2) and an interpretation component 320.The interpretation component 320 can be configured to interpret abarcode value of the tag 310 from a response of the tag to the magneticfield, where the tag response is based, at least in part, on value andplacement of a set of capacitors of the tag. The magnetic field of theloop 210 can interact with the tag 310 and the tag 310 can produce aresponse from this interaction. The loop 210 can receive this responseand the response can be interpreted by the interpretation component 320.This response can be based on the placement and/or value of individualcapacitors of the tag 310 such that the tag is identifiable as a barcode.

In one embodiment, a tuner component can be employed to select thevalues of the individual capacitors of the set of capacitors a-h of FIG.1 such that the electric field is minimized. The individual capacitorsof the set of capacitors a-h of FIG. 1 can be uniform in value or notuniform in value (e.g., each capacitor has distinct value and/or atleast one capacitor has a value different from another capacitor). Inone embodiment, the tuner component can select values of individualcapacitors of the tag 310 such that the tag is an identifiable barcode.In one example, arrangement (e.g., number and spacing) of the individualcapacitors as well as the values of the individual capacitors can bepart of the identifiable barcode.

In one embodiment, the trial and error can be used to create a databaseof optimal capacitor values (e.g., to create strongest magnetic field,to create smallest electric field, for barcode usage, etc.). Selectioncan comprise identifying a desired characteristic of the loop 210 (e.g.,smallest electric field along a longitudinal axis of the loop 210) andreading the database values. This can be compared with availablecapacitor values and values can be selected and implemented. In oneembodiment, the tuner component 310 can select a frequency for the loop210 (e.g., a frequency between 1 MHz and 1 gigahertz) such that theelectric field is minimized. In one embodiment, the tuner component canread an instruction for capacitor values for the individual capacitorsof the tag 310 and set the values accordingly.

FIG. 4 illustrates one embodiment of a system 400 with a transmissionloop 410 and a reception loop 420. An area between the transmission loop410 and the reception loop 420 can be a strongest area to identify anobject of interest. In one example, a metal object between the loops 410and 420 can give a stronger reading than the metal object betweenoutside the loops 410 and 420 (e.g., to the side of the loops, behindthe receiving loop, etc.). Thus, the two loops 410 and 420 can be usedtogether as a detector and be powered by a current source 430.

Various items can be associated with the system 400 that facilitatesperformance of the system 400 as a successful detector. The receptionloop 410 can be associated with a loop tuner 440 and a spectrum analyzer450. The spectrum analyzer 450 can interpret results from a loop, suchas the transmission loop 420 or the loop 210 of FIG. 2. In oneembodiment, the spectrum analyzer 450 can be configured to identify apresence of an object (e.g., metal or dielectric) between the receptionloop 420 and the transmission loop 410. The presence can be determinedthrough interference of the magnetic field from the transmission loop410 to the reception loop 420. Thus, how the magnetic field differs fromleaving the transmission loop 410 to being received by the receptionloop 420 can be used by the spectrum analyzer 450 to determinedetection. The spectrum analyzer 450 can be configured to identify apresence of an object near one of the loops (e.g., on the side of thereception loop 420 that does not face the transmission loop 430) by wayof magnetic field observance. The spectrum analyzer 450 can also beconfigured to cause an output indicative of the presence (e.g., cause alight to flash, send a communication, etc.). The spectrum analyzer 450can function at a set value, such as at 50 ohms. Since the transmissionloop 420 or the loop 210 of FIG. 2 can function at lower resistancelevels, the loop tuner 440 can be employed to match output of thereception loop to 50 ohms. Therefore, the loop tuner 440 can function tomatch impedance. In one embodiment, the reception loop 420 matches thetransmission loop 410 (e.g., is identically structured). The receptionloop 420 can receive the magnetic field. Thus, the transmission loop 410and reception loop 420 can form a detector. A detectable object, such asa metal or dielectric penetrates the magnetic field such that themagnetic field becomes modified. Modification of this field can beidentified by the spectrum analyzer 450 and be used to identifyexistence of the object.

While the system 400 is shown with one transmission loop 410 and onereception loop 420, other configurations can be implemented. In oneexample, two receiving loops 420 can be used—one loop 420 on one side ofthe transmission loop 410 and one loop 420 on the other side. Data fromthe reception loops 420 can be merged by a differential amplifier andthen fed to the loop tuner 440 and/or the spectrum analyzer 450 (e.g.,the differential amplifier can be part of a device that includes theloop tuner 440, the differential amplifier can be part of the loop tuner440, the differential amplifier functions on output of the receptionloop 420 after the loop tuner 440 functions on the output, etc.). Thedigital amplifier can merge data (e.g., output) from the multiple loopsso the spectrum analyzer can treat the data one set of data.

FIG. 5 illustrates one embodiment of a system 500 comprising a loopantenna 510 and a current source 430. In one embodiment, the loopantenna 510 (e.g., rectangular loop antenna) is a small loop antennasuch as a singular small loop antenna (one loop) or a multiple smallloop antenna (more than one loop). The loop antenna 510 can be poweredby a current (e.g., a current of at least one amp) produced from thecurrent source 430. The current source 430 can be a low impedancecurrent source (e.g., a current source operating at less than about 25ohms with a frequency of at least 1 MHz). The loop antenna 510 cancomprise a set of wire segments that are individually divided by a setof capacitors such that two individual capacitors are separated by asegment of wire and two individual capacitors are separated by acapacitor. This configuration of the loop antenna 510 can be theconfiguration of the system 100 of FIG. 1 and/or the can function as theloop 210 of FIG. 2. The loop antenna 510 can produce an electric fieldand a magnetic field such that the magnetic field, that extendssubstantially normal to a plane of the loop antenna 510, issubstantially greater than the electric field. The electric field can beof a level that does not substantially interfere with communicationequipment (e.g., does not hinder communication equipment fromfunctioning, does not provide a noticeable disturbance to communicationequipment, etc.) and the magnetic field can be of a high enough level todetect a metal beneath a surface.

In one embodiment, the loop antenna 510 can form a loop that is poweredby the current source 430 with a current of at least two amps. Whensupplied with the current the loop antenna 510 produces a magnetic fieldthat is substantially greater than the electric field. Throughout theloop antenna 510 the magnitude and phase can be kept substantiallyconstant. In one example, the magnitude is keep substantially constantthroughout the loop such that the magnitude change is not greater thanthat which is produced by no more than one of the wire sections and aphase is keep substantially constant throughout the loop such that thephase change is not greater than that which is produced by no more thanone of the wire sections. Thus, when phase and/or magnitude change isimpacted by a wire section (e.g., a largest wire section), the capacitoroffsets that change before the next wire section is impacted.

The loop antenna 510 can comprise a first wire section (e.g., wiresection 2 of FIG. 1), a second wire section (e.g., wire section 3 ofFIG. 1), and a third wire section (e.g., wire section 4 of FIG. 1).These wire sections can be distinct from one another (e.g., not the samewire section) and be in series with one another (e.g., the first wiresection and the third wire section are not contiguous). The loop antenna510 can also comprise first capacitor (e.g., capacitor b of FIG. 1) thatdivides the first wire section from the second wire section as well as asecond capacitor (e.g., capacitor c of FIG. 1) distinct from the firstcapacitor that divides the second wire section from the third wiresection and that is distinct from the first capacitor. The firstcapacitor can have a value that causes the electric field to beminimized and the second capacitor can have a value that causes theelectric field to be minimized. The first capacitor can offset animpedance of the first wire section while the second capacitor canoffset an impedance of the second wire section. Thus, impedances of thewire sections can quickly be offset by the capacitors throughout theloop antenna 510.

In one embodiment, the magnetic field extends about one wavelength fromthe loop antenna 510. In one example, the loop antenna 510 can functionwith a frequency of about 13.56 MHz and as such the wavelength can beabout 22 meters. The loop antenna 510 can be a singular small loopantenna that performs transmission and reception functions. The magneticfield from the loop antenna 510 can be of a sufficient strength todetect a metal beneath a dielectric (e.g., beneath ground) while theelectric field is low enough as to not substantially impact acommunication device.

The current source 430 can be converted into a power amplifier and thenthe power amplifier can be converted back into a current source. In oneembodiment, the current source 430 can comprise a 1 kilowatt RFGenerator Module and the loop tuner 440 of FIG. 4. The RF GeneratorModule can be modified to match low input impedance of the loop antenna510. The RF Generator Module can comprise a set of transistors thatfunction as a voltage controlled current source. In addition, the RFGenerator Module can comprise an oscillator (e.g., 13.56 MHz oscillator)or oscillator can be removed and the current source 430 can be connectedto a signal generator that facilitates use of different pulsingwaveforms. In one embodiment, the current source 430 employs a sweptsignal.

FIG. 6 illustrates one embodiment of a system comprising the loopantenna 510, an analysis component 610 and a message component 620. Inone embodiment, the loop antenna 510 can function with a tag (e.g., aradio frequency identification tag). The tag (e.g., physically separateand distant from the loop 510) can produce an output in response tobeing subjected to the magnetic field. The analysis component 610 can beused to perform an analysis of this output from the tag. The messagecomponent 620 can produce a message that is based, at least in part, ona result of the analysis. In one example, the message is a lightflashing that the tag is located and/or identification information ofthe tag (e.g., when the tag functions as a barcode). In one embodimentthe tag is a loop itself (e.g., separate from the loop antenna 510 andconfigured similarly to the loop antenna 510). Capacitors of the tag canhave different values and/or a different number of capacitors from theloop antenna 510. The arrangement and/or values of the tag capacitorscan represent information similar to that contained in a barcode and assuch the tag can be used as an identification device that can beinterpreted by the system 600. The tag can be a passive tag (e.g.,totally passive tag) that functions as an asset management tag. Thefrequency of the magnetic field of the loop antenna 510 can provideadditional information that can be provided to the tag. In oneembodiment, the tag and loop antenna 510 can work together to create acurrent that is rectified to provide direct current that powers anactive circuit (e.g., an active circuit connected to the tag). A circuitof the tag can alter characteristics of the loop antenna 510 (e.g., thetag employs the transistor switch 220 of FIG. 2 to changecharacteristics of the loop antenna 510). If characteristics of the loopantenna 510 are altered in a binary fashion by the tag, then the tag canreturn binary information in a trailing phase characteristic that isrecognized by the analysis component 610. In one embodiment, the tag canbe battery powered and operate as a semi-passive tag.

FIG. 7 illustrates one embodiment of a loop 700 with an x-axis, a y-axisand a z-axis. The loop 700 can be raised above the ground plane (e.g.,free space or ground with finite conductivity). The designation of ‘o’of the loop 700 can be the source and the designations of ‘x’ of theloop 700 can be capacitor loads. The magnetic field can be substantiallygreater than the electric field down the x-axis such that it is thelongitudinal axis of loop 700.

FIG. 8 illustrates one embodiment of a system 800 comprising a processor810 and a non-transitory computer-readable medium 820. In one embodimentthe non-transitory computer-readable medium 820 is communicativelycoupled to the processor 810 and stores a command set executable by theprocessor 810 to facilitate operation of at least one componentdisclosed herein (e.g., the interpretation component 320 of FIG. 3). Inone embodiment, at least one component disclosed herein (e.g., theanalysis component 610 and/or the message component 620 of FIG. 6) canbe implemented, at least in part, by way of non-software, such asimplemented as hardware by way of the system 800. In one embodiment thenon-transitory computer-readable medium 820 is configured to storeprocessor-executable instructions that when executed by the processor810 cause the processor 810 to perform a method disclosed herein (e.g.,the methods 900 and 1000 discussed below).

FIG. 9 illustrates one embodiment of a method 900 comprising sevenactions. At 910 portions are selected for a loop such as a number ofcapacitors and a number of wire segments to be used in the loop. Otherselections can be made such as length of the segments and in turn theoverall size and/or shape of the loop. These selections can be based onuser instruction, based on a desired output (e.g., for a set barcodeconfiguration), etc. With these selections made the loop can beconstructed at 920.

An observation can be made on how the loop is ultimately constructed at930 and values for the capacitors can be selected at 940. In oneexample, based on physical characteristics of the loop specific defaultcapacitor values can be selected from a database. With the valuesselected the loop can be tested at 950 and a determination can be madeat 960 if results are acceptable such as if the magnetic field is strongenough, if the electric field is weak enough, if the loop isidentifiable as a barcode, etc. If results are acceptable from theselected values, then the selected values can become the values for theloop at 970.

If results are not acceptable, then the values can be reselected and themethod 900 can return to action 940. In one example, a series ofselections can be made at 940 and ultimately a selection that produces abest result (e.g., highest magnetic field with the lowest electricfield) can be selected. This best resulting selection can be implementedfor the loop at 970.

FIG. 10 illustrates one embodiment of a method 1000 comprising sixactions. The method 1000 can be employed in producing a loop that canfunction as a barcode. Parts can be chosen at 1010 including a number ofcapacitors, a number of wire sections, length of the wire section, brandof the capacitors, tolerance of the capacitors, etc. Along with choosingparts, a configuration can be selected at 1020. The configurationselection can be how far spaced capacitors are from one another, ifspacing is uniform or non-uniform, etc. Part choice and configurationselection can take place concurrently and/or in conjunction with oneanother. In one example, selection of the number of capacitors can beselected in view of how the capacitors are to be spaced from oneanother.

The loop can be built at 1030 with the parts chosen at 1010 inaccordance with the configuration selected at 1020. Values for thecapacitors can be selected at 1040 with the goal of producing a specificbarcode in view of the parts and configuration. The values can be set at1050 and the loop can be deployed. Actions of methods disclosed hereincan be practiced in a different order than disclosed when practical,such as the values being selected and set before construction of theloop.

What is claimed is:
 1. A system, comprising: a set of wire sections; anda set of reactive compensation elements, where the set of wire sectionsand the set of reactive compensation elements are configured to form aloop powered by a current provided by a current source operating atabout 1 megahertz or above with a source impedance of about 25 ohms orless, where the individual reactive compensation elements and theindividual wire sections of the set of wire sections alternate with oneanother, where the set of reactive compensation elements function tokeep a magnitude and a phase of the current substantially uniformthroughout the loop, and where the loop, when powered by the current,produces a magnetic field that is substantially greater than a electricfield along a longitudinal axis of loop.
 2. The system of claim 1, wherethe magnetic field is of a sufficient strength to detect a metal.
 3. Thesystem of claim 1 where the magnetic field is of a sufficient strengthto detect a dielectric.
 4. The system of claim 1, where the magneticfield extends about one wavelength from the loop and contacts a tag toprovide the tag with wireless energy.
 5. The system of claim 1, wherethe individual reactive compensation elements of the set of reactivecompensation elements are substantially evenly distributed from oneanother and where the current of the current source is of at least abouttwo amps.
 6. The system of claim 1, where characteristics of the loopare altered in a binary manner such that direct current is produced andwhere the direct current powers an active circuit wirelessly.
 7. Thesystem of claim 1, where loop is configured to perform transmission andreception functions.
 8. The system of claim 1, comprising: an analysiscomponent configured to perform an analysis on an output provided from atag, where the output is a response of the tag being subjected to themagnetic field; and a message component configured to produce a messagethat is based, at least in part, on a result of the analysis.
 9. Thesystem of claim 1, where the loop constitutes a small loop antenna. 10.The system of claim 1, where the loop is a transmission loop, where areception loop matches the transmission loop, where the reception loopreceives the magnetic field, and where the transmission loop andreception loop form a detector.
 11. The system of claim 10, comprising:a spectrum analyzer configured to identify a presence of an objectbetween the reception loop and the transmission loop and configured tocause an output indicative of the presence, where the presence isdetermined through interference of the magnetic field from thetransmission loop to the reception loop.
 12. The system of claim 1,comprising: an interpretation component configured to interpret abarcode value of a tag from a response of the tag to the magnetic field,where the response is based, at least in part, on value and placement ofa set of capacitors of the tag.
 13. A singular loop antenna, comprising:a first wire section; a second wire section that is distinct from thefirst wire section; a third wire section that is distinct from the firstwire section and distinct from the second wire section, where the firstwire section and the third wire section are not contiguous; a firstreactive compensation element that divides the first wire section fromthe second wire section; and a second reactive compensation element thatdivides the second wire section from the third wire section and that isdistinct from the first reactive compensation element, where the firstwire section, the second wire section, the third wire section, the firstreactive compensation element, and the second reactive compensationelement form at least part of a loop powered by a current of at leasttwo amps supplied from a low impedance current source, where thesingular loop antenna, when supplied with the current, produces amagnetic field that is substantially greater than the electric fieldalong a longitudinal axis of the singular loop antenna, where the firstreactive compensation element offsets an impedance of the first wiresection, where the second reactive compensation element offsets animpedance of the second wire section, where a magnitude is keepsubstantially constant throughout the loop such that the magnitudechange is not greater than that which is produced by no more than one ofthe wire sections, and where a phase is keep substantially constantthroughout the loop such that the phase change is not greater than thatwhich is produced by no more than one of the wire sections.
 14. Thesingular loop antenna of claim 13, where the magnetic field extendsabout one wavelength from the loop, where a frequency of the singularloop antenna is between about 1 Megahertz to about 1 Gigahertz, wheresingular loop antenna performs transmission and reception functions, andwhere the singular loop antenna is a singular small loop antenna. 15.The singular loop antenna of claim 14, where the magnetic field is of asufficient strength to detect a metal, where the first reactivecompensation element has a value that causes the electric field to beminimized, where the second reactive compensation element has a valuethat causes the electric field to be minimized, and where the electricfield low enough as to not substantially impact a communication device.16. The singular loop antenna of claim 15, where characteristics of theloop are altered in a binary manner such that direct current is producedand where the direct current powers an active circuit wirelessly.
 17. Asystem, comprising: a current source that functions at under about oneohm with a frequency between about 1 megahertz and 1 gigahertz; and asingular small loop antenna that is powered by the current, the singularsmall loop antenna comprises a set of wire segments that areindividually divided by a set of reactive compensation elements suchthat two individual reactive compensation elements are separated by asegment of wire and two individual reactive compensation elements areseparated by a reactive compensation element and the singular small loopantenna produces an electric field and a magnetic field such that themagnetic field, that extends substantially normal to a plane of thesingular small loop antenna, is substantially greater than the electricfield and the electric field is of a level that does not substantiallyinterfere with communication equipment.
 18. The system of claim 17,where the magnetic field is of a high enough level to detect a metalbeneath a surface.
 19. The system of claim 17, where the current sourcecomprises a radio frequency generator module that matches inputimpedance of the singular small loop antenna and where the radiofrequency generator module comprises a set of transistors that functionas a voltage controlled current source.
 20. The system of claim 17,comprising: an analysis component configured to perform an analysis onan output provided from a tag, where the output is a response of the tagbeing subjected to the magnetic field; and a message componentconfigured to produce a message that is based, at least in part, on aresult of the analysis.